This invention relates to an improved process for the electrolytic oxidation of appropriately substituted cresol salts to produce the corresponding methyl-methyl coupled dehydrodimeric cresols. More particularly, this invention relates to an improved process for the electrolytic oxidative methyl-methyl coupling of cresol salts substituted with non-interfering, blocking substituents at least at the 2,4,6-positions relative to the phenolic oxyanion where at least one of the substituents is the cresolic methyl to produce methyl-methyl coupled dehydrodimeric cresols, or simply 1,2-bis(hydroxyaryl)ethanes.
The electrolytic oxidation of cresol salts substituted with non-interfering, blocking substituents at least at the 2,4,6-positions relative to the phenolic oxyanion where at least one of the substituents is the cresolic methyl to produce methyl-methyl coupled dehydrodimeric cresols is taught in copending application, Ser. No. 646,725, filed Jan. 5, 1976 to Richard C. Hallcher and entitled "Electrolytic Oxidative Methyl-Methyl Coupling of Cresol Salts," which application is assigned to the same assignee as in the present case.
Oxidative methyl-methyl coupling of cresols has previously been accomplished particularly to prepare the corresponding 1,2-bis(hydroxyaryl)ethanes, by the use of a variety of oxidizing agents. For example, oxidizing agents such as alkaline potassium hexacyanoferrate(III), lead(IV)oxide, silver oxide, air in cumene containing iron(III)stearate, air in chlorobenzene containing 2,2'-azobis(2-methylpropanenitrile)(.alpha. ,.alpha.'-azobisisobutyronitrile), organic peroxides, and the like have been used for this purpose. Each of these known reagents have certain disadvantages when used in this reaction. These may include low yield, simultaneous production of contaminating by-products such as stilbenequinone structures, and the necessity of using extremely dilute solutions and long reaction periods. Moreover, some of the reagents are relatively expensive.
The disadvantages encountered in the prior art chemical oxidative methyl-methyl coupling processes are overcome by the discovery that appropriately substituted cresol salts undergo electrolytic oxidation to produce methyl-methyl coupled dehydrodimeric cresols [1,2-bis(hydroxyaryl)ethanes].
The improvement of the present invention rests in the discovery that an unexpected surprisingly greater yield of methyl-methyl coupled dehydrodimeric cresol product can be obtained by conducting the electrolysis in a liquid electrolysis medium comprising the cresol salt, the corresponding free cresol, and solvent, wherein the molar equivalent ratio of cresol salt to free cresol is no more than about 1.0 molar equivalent of cresol salt to about 5.0 molar equivalents of free cresol.
Various other advantages of this invention will become apparent from the accompanying description and claims.